Preparation of nitrogen-and phosphorous co-doped carbon microspheres and their superior performance as anode in sodium-ion batteries

Sodium-ion batteries are considered a top alternative to lithium-ion batteries for large-scale renewable energy storage units due to their low cost and the abundance of sodium-bearing precursors in the earth's mineral deposits. However, the absence of a suitable negative electrode material hinders their development. In this contribution, we report the preparation of nitrogen and phosphorous co-doped carbon microspheres through a hydrothermal process followed by heat treatment in presence of (NH₄)₂HPO₄ and investigate their electrochemical performance as anode in sodium-ion batteries. Benefiting from the N, P co-doping, the obtained N, P co-doped carbon microspheres demonstrates high specific capacity, excellent cycle stability as well as good rate performance. The as prepared N, P co-doped carbon microspheres can deliver a reversible capacity of 305 mAh g^-1 at a current density of 0.1 A g^-1 and even deliver a capacity of 136 mAh g^-1 at 5 A g^-1. This superior sodium storage performance of N, P co-doped carbon makes it as a promising low-cost anode candidate for sodium-ion batteries.